In general, examples of known leaching operations for copper sulfide ores via hydrometallurgy include a leaching operation comprising performing an agitated batch reaction with the use of sulfuric acid or hydrochloric acid and a leaching operation (heap leaching method) of forming ore heaps, supplying sulfuric acid or hydrochloric acid to the tops of the ore heaps, and recovering liquid dripping therefrom due to the force of gravity. However, since chalcopyrite and enargite are very poorly soluble in mineral acids, the leaching rate during leaching at an ordinary temperature with the use of such ores is very slow, which is problematic. In addition, at an advanced stage of a leaching reaction, the leaching rate is significantly lowered due to leaching inhibition caused by a coat formed on the ore surface with an iron precipitate and the like, which is also problematic.
Hence, a variety of techniques for increasing the rate for leaching a copper sulfide ore containing chalcopyrite, enargite, or the like as a main constituent with the use of a mineral acid have been suggested. In one reported example, leaching is carried out by adding activated carbon and iron to a leaching solution and maintaining the oxidation-reduction potential (Ag—AgCl reference electrode) at 350 to 450 mV (JP Patent Publication (Kokai) No. 2005-15864 A). Alternatively, methods involving pressurization to an atmospheric pressure or more, heating to 100° C. or more, and the like for leaching have been reported (JP Patent Publication (Kokai) No. 2003-328050 A, JP Patent Publication (Kohyo) No. 2001-515145 A, and JP Patent Publication (Kokai) No. 10-317072 A (1998)). However, such leaching involving heating, pressurizing, or the like is problematic in terms of cost increase, although such leaching is effective for the improvement of the leaching rate.
Meanwhile, examples in which iodine is used as an oxidant for metal leaching have been reported. A typical example of such leaching is a method of producing gold with a high purity comprising dissolving gold in a solution containing an iodine compound comprising, for example, iodine and potassium iodide and carrying out reduction precipitation of gold (JP Patent Publication (Kokai) No. 64-17826 A (1989)). In addition, a method of dissolving a noble metal with the use of a dissolving solution containing at least one organic solvent or the like selected from the group consisting of iodine and/or iodide ions, polyalcohol, polyether, and cyclic lactone has been also reported (JP Patent Publication (Kokai) No. 2005-154892 A). However, it is necessary to use iodine (I2) at a high concentration in this method, and thus an organic solvent must be used as a solution for dissolving iodine (I2).